Any suggestions on how to improve the upper part of the shot? all of the gear info is included in the link.Personally i think it's because of the acrylic dome port.. but i could be wrong.Any tip is welcome.

Looks like there may still be a sheet of water on the dome to shoot through. You can get all kinds of interesting effects doing this.

Steve

In this shot, i tried to get a traditional split shot, with the top part being reasonably sharp. so this picture is not really a big succes.
I took this one at the end of the dive (at the exit point) so there was still a lot of water on the dome indeed.

Next time i will try to make a split shot in the beginning of the dive when the dome is still dry.
Thank you!

I think that you have to go into the water to take splits, not try them at the end of the dive. Glass domes and water repellant are helpful: even spit works. If not: Photoshop, before it becomes a professional-only product!

I've also found that using a portrait format (and even focussing on the background) can sometimes yield a better image: